This invention relates to an automatic monitoring and/or control system for liquid/solid separation processes, particularly dewatering processes wherein dewatering is aided by the addition of a dewatering aid such as a polymer or other flocculant. A method of monitoring and/or controlling separation performance is also disclosed.
More particularly, this invention relates to the use of one or more photodetectors to monitor the performance of a liquid/solid separation process and to adjust additive feedrates in accordance with the separation efficiency readings so obtained, thereby controlling liquid/solid separation performance.
Liquid/solid separation processes are used to effect the transition of a two-phase composition from an initial liquid/solid state, wherein the liquid:solid weight ratio is high (e.g., a dilute slurry), to a state where some portion of the liquid medium has been removed from the solid medium, thereby lowering the liquid:solid weight ratio to a second value. As this transition occurs, the surface appearance of the composition being dewatered changes, as does the amount of light reflected by the surface of the two-phase composition being treated changes as the liquid:solid weight ratio decreases.
One or more photo detectors can be used to detect variations in the intensity of light reflected by a stream being dewatered as the stream changes from its original, wet state, to a "dewatered" state. As used herein, the term "dewater" refers generally to the separation of a liquid phase from a liquid phase/solid phase composition. Use of this term does not imply that the liquid being separated is water, though in a majority of instances the liquid being removed is water.
If sufficient dewatering occurs to substantially remove free liquid, a "dry line" may appear somewhere across the surface of the material being dewatered. In such instances, one or more photodetectors can be used to monitor the location of the dry line. Thus, a liquid/solid composition may initially contain substantial free liquid. Prior to dewatering, the surface of such a composition may be mirror-like. As dewatering occurs, and free liquid is removed, the irregular surface of the solid material has different reflective properties than does the mirror-like surface of the wet composition, such distinct reflective properties can be readily discerned by photodetectors.
A photodetector can therefore be used to monitor and/or a control separation process by correlating signal variations, which are attributed to the intensity of the light viewed by the photodetector, to dewatering performance. For example, a high/low voltage signal from a photodetector can be used to advise an operator as to the location of a system's dry line relative to the location of a detector. Additionally, such a signal can be modified to a signal which is proportional to the amount of dewatering which has occurred up to the point on the dewatering surface where the photodetector reading is being made. In the broadest sense, the instant invention can be utilized to monitor and/or control any unit operation which acts on a composition so as to affect the reflective properties of the surface of the composition, if such distinctions can be discerned by a photodetector.
As an example of an industrial application, a photodetector may be used to monitor a belt-filter press dewatering system and to control the flocculant feed rate to such a system. Polymers or other flocculants are added to enhance dewatering; for this reason, dewatering efficiency can be regulated by controlling additive dosage.
Additionally, the instant invention may be used to determine the drainage efficiency of paper pulp in a paper-making process, such as in the wet end forming section of a paper plant. Specific uses may be found relative to Fordrinier tables, twin-wire machines, cylinder machines and other sheet-forming equipment.
However, the instant invention may be used to monitor and/or control the operation of any liquid/solid separation process or apparatus, including, but not limited to drying processes, filtration processes (such as vacuum filtration) and gravity dewatering processes.
While all of these examples relate to suggested uses of the claimed invention, they are in no way intended to limit the scope of the instant invention.
It is therefore an object of this invention to provide a method and system for monitoring and/or controlling a liquid/solid separation process, particularly when the transition of the composition being treated from an initial state having a high liquid:solid weight ratio to a second state having a lower liquid/solid weight ratio is dependent upon a process variable such as the addition of a flocculant. The instant system and method control additive dosage and/or other process variables, and thereby control separation performance.
A further object of this invention is to provide method and system which controls and/or monitors a liquid/solid separation process by correlating a standard analog or digital signal from a photodetector to a signal which is proportional to dewatering efficiency.
A further object of this invention is to reliably monitor and/or control a liquid:solid separation process under varying feed conditions.
A further object of this invention is to measure the efficacy of a liquid/solid separation process instantaneously and accurately.
A further object of this invention is to quickly monitor and/or control liquid/solid separation system upsets.
A further object of this invention is to provide a monitoring and/or control system which is inexpensive and which is easily maintained.
A further object of this invention is to minimize flocculant consumption.
A further object of this invention is to control additives fed to dewatering processes wherein feedstream parameters, such as solids concentration, vary.
A further object of this invention is to maximize througput of a separation process.
A further object of this invention is to improve the operability of systems which are difficult to control.
A further object of this invention is to reduce operator attention.
Still further, it is an object of this invention to control additive feedrates to belt-filter press dewatering systems.
Further objects will become apparent from the description which follows.
U.S. Pat. No. 4,587,023 discloses a method of monitoring and controlling belt press separation systems which utilizes a level detector, such as an ultrasonic level detector, to measure separation performance.